In such eyeglass frames one end of one of the open rims forms the nut of the assembly and the other end of the rim forms an insert which is freely traversed by the shank of the screw itself.
The underside of the machine screw and the insert together define transverse bearing surfaces. The bearing surfaces are urged together for clamping the rims around the corresponding lenses.
The insert member is fixed against rotation relative to the nut member since it is part of the same rim as the nut but is axially displaceable relative to the nut against the biassing means which tend to keep the insert away from the nut and which are defined by the inherent resilience of the rim itself. The base transverse bearing surface formed on the insert engages the transverse bearing surface formed on the underside of the head of the screw. The biassing means tend to urge the lugs away from each other.
One of the problems posed with the holding of such screw assemblies of eyeglass frames is to assure long-lasting clamping necessary to prevent accidental loss of lenses while permitting, whenever necessary, the removal of lenses for their replacement.
It is of course well known at the present to provide such screw assemblies with self-locking means thereby satisfying the first-mentioned requirement. But any disassembly of such machine screw assemblies with self-locking means has meant damaging one of the component parts of the assembly which must then be repaired or even replaced if subsequent reassembly is desired.
Such is the case, for example, with the arrangement disclosed in French printed patent application No. 2,204,816 in which it is proposed to locally flange part of the insert member against the screw which extends therethrough, the insert member forming for this purpose an annular member around the head of the screw.
Further, in some arrangements an additional part of the nut locking variety must frequently be used thereby complicating the steps of assembly, disassembly and reassembly and increasing the cost of such a screw assembly.
This is the case with U.S. Pat. No. 3,438,416, for example, in which waved surfaces are provided on the underside of the screw and the washer, the washer being initially free for rotation in relation to the nut with which the screw must threadedly engage. Moreover, this screw assembly is not intended to be used for closing the open end of an eyeglass frame rim.